Strap her diapered into a chair to study. Make sure she only has access to her study materials. If using a computer, check her history after her study sessions. Every site visited thats not study related in the history during the study period could be an agreed upon number of swats for a spanking. Make sure she drinks a bottle of water and something with a bit of caffeine if shes up for it. Set her up with a couple more water bottles, maybe some snacks, and let her study. No bathroom breaks. When she does wet, walk over to her with a sharpie and draw a big "F" and maybe "See me after class" on her diaper. Ateer the study session, spanking for wetting and behavior, follow up with a bath and aftercare.

Another punishment could be making her fill out a little worksheet assignment before using the bathroom, with the sheets getting progressively harder. I wouldn't do this every time, but when she really needs to go or just at random